Method of preserving rubber and product thereof



Patented Jan. 15, 1952 METHOD OF PRESERVING RUBBER AND PRODUCT THEREOF Marion W. Harman, Nitro, W.,Va., assignor to Monsanto Chemical Company, St. Louis, Mo., a

corporation of Delaware No Drawing. Application January 17, 1949, Serial No. 71,399

. 18 Claims. (Cl. 260-803) 1 This invention relates to the treatment 01 rubber and more particularly to the use in rubber and rubber-like materials of improved antioxidant compositions.

It has long been known that deterioration due to heat, light, oxygen, and flexing in natural and synthetic rubber stocks can be materially re-' duced by incorporating in the rubber stock, either before or after vulcanization, the condensation product of an aliphatic ketone and an aromatic amine. The condensation products of aniline and acetone, of oand p-amino biphenyl and acetone, of diphenyl amine and acetone, and of phenyl naphthylamine and acetone, are among the more widely known rubber antioxidants and while these and other more expensive ketoneamine condensation products produce goodresuits, the industry has constantly sought improvements.

The chief objects of this invention are to'provide the art with a new and improved antioxidant composition; to' provide the art with a new composition possessing superior antiflex-cracking properties; to provide the art with a readily dispersible, economical, and eilicient rubber antioxidant composition; to make more eflicient use of aliphatic ketone-aromatic amine, condensa-,

tion products. Further objects will be apparent from the following description.

It has been found in accordance with this invention that a synergistic eiiect is obtained by employing an aliphatic ketone-aromatic amine condensation product in conjunction with a product obtained by reacting a hydroxy aromatic hydrocarbon with an N-(2-thiazyl thio methyl) urea of the general formula 2 than either component and beyond the mere additive eflect of the proportions of the individual components.

As exemplary of the invention the following specific embodiments are illustrative and are not to be construed as limitative thereof.

EXAIWPLEI To a 3-neck flask equipped with a stirrer. a thermometer, and an air cooled reflux condenser were charged 209 parts by weight (substantially 0.5 mol) of his N,N'-(2-benzothiazyl thio methyl) urea and 188 parts by weight (substantially 2.0 mols) of phenol. The reaction flask was then placed in an oil bath and heated for minutes at a temperature of 175-180 C. Vacuum was applied to the reaction mix and approximately 102 parts by weight (substantially 1.1 mols) of phenol was recovered. Approximately 284 parts Y by weight of a brown sticky resinous product was obtained. This resinous substance was soluble in dilute caustic, benzene, acetone, and in alcohol and believed to consist principally of a product containing approximately 1.7 mols of phenol per mol of his N,N'-(2-benzo thiazyl thio methyl) urea.

EXAMPLE 2 To a suitable reaction vessel equipped with an air condenser, a thermometer, and stirrer were charged 104.5 parts by weight (substantially 0.25 mol) of bis N,N-(2-benzothiazyl thio methyl) urea and parts by weight (substantially 1.0 mol) of hydroquinone. The reaction vessel was then placed in an oil bath and heated for 3 hours at 175-180 C. Upon cooling 201.7 parts by weight of a gummy mass was obtained. This product was taken up with alcohol and filtered. Upon addition of water to the filtrate a black tarry resin settled out. The-resin was then dried by heating in an oil bath at C. at reduced pressure. 116.7 parts by weight of a brittle black resinous material was obtained which was soluble in caustic soda, alcohol, acetone, and ethyl acetate.

aosacaa EXAMPLE 3 washed with water, and filtered. The filtrate 1 was acidified with dilute sulfuric acid and a brick red gummy substance developed which gradually turned into a brittle resin. Upon removal of residual acid the product, 139.3 parts by weight of a brick-red resin, was found to have a melting point range of 155-165 C. The product was soluble in dilute caustic, acetone, and alcohol.

The above prepared resinous materials were mechanically mixed with the p-amino biphenylacetone condensation product described by J. R. Ingram, U. S. Patent 2,062,885, and the mixture incorporated in the usual manner in a typical stock suitable for the tread portion of an auto mobile tire comprising densation product with the reaction product of a hydroxy aromatic hydrocarbon and an N-(2- thiazyl thio methyl) urea. Compositions B, C and D were markedly superior in flex-cracking resistance to stock A as evident from Table II below. Test pieces were cut from the above described vulcanized rubber stocks and artificially aged for 9 hours at 121 C. in an air bomb under 80 lbs/in. pressure. The flex-cracking resistance of these aged specimens was then determined by a flexing machine as set forth by L. V. Cooper, Analytical Edition of Industrial and Engineering Chemistry, vol. 2, No. 4, pp. 391-394. The flexing data are as follows:

' These improved antioxidant compositions are readily dispersible in vulcanized as well as un- A B 0 D E Parts by Paris by Pans by Paris by Parts by weight weiyht weigh! weight weight Smoked sheetsrubber 100 lUO 100 100 100 Carbon black 50 50 50 50 Zinc oxide." 5 5 5 5 5 Pine tar 2 2 2 2 2 Stearic acid 3 3 3 3 3 Sulfur..." 3 3 3 5i 3 lylercaptobenzothiazole 0.75 0.75 0.75 0.75 0.75 pAmino biphenyl-acetone condensation product 1.0 0.5 0.5 0.5 Phenol-bis N,N'-(2-benzothiazyl thio methyl) urea brown resinous reaction product of Example 1 0.5 Hydroquinone-bis N,N'-(2-benzo thiazyl thio methyl) urea brittle black resinous reaction product of Example 2. 0. 5 Resorcinol-bis N,N-(2-bcnzo thiazyl thio methyl) urea red resinous reaction product of Example 3 0. a

The above rubber stocks so compounded were vulcanized rubber, both natural and synthetic, then vulcanized by heating in a press for and present no compounding problem. minutes and minutes respectively at C. Other ketone-amine condensation products Test strips were cut from the vulcanized stocks Which possess antioxidant properties such as and artificially aged in an air bomb for 6 and 9 aniline-acetone, toluidine-acetone, napthylhours, respectively, at 121 C. and under a presamine-acetone, anisidine-acetone, phenetidinesure of 80 pounds per square inch. The physical acetone,' diphenylamine-acetone, dinaphthyltest data of the respective stocks is set forth amine-acetone, phenyl naphthylamine-acetone, below. and the like, or mixtures thereof, when employed Table I in conjunction with the reaction product of a hydroxy aromatic hydrocarbon and an N-(2- Unaged Tonsihrsmmh thiazyl thio methyl) urea produce antioxidant aft er aging 111 Compositions characterized by a pronounced synk Min. igio dums u U ig zl ergistic effect and ready dispersibility in natural Stoc cure at s. in?) a F t. Y ti- "z 135 C. elongations ol- Elong, mate Li) and synthet'lc rubber er- 115110, As further exemplary of the invention the folcent s.;in. 300% 500% shows 91mm lowing embodiment s llustrative and in nowise is to be consldered limitative thereof.

A to 1,593 3, 270 003 4.1120 2,110 1,523 B 00 p733 5,750 580 4,4117 3.62:; 2.1194) EXAMPLE 4 g 00 1,813 3,793 52 7 1. 023 3.0a, H

00 1,1107 2,727 5. 77 r ,14 K 60 1,607, M67! 00 4,5) mm 693 The crude brown sticky resinous product of A 90 "27 4,723 L593 Example 1 was taken up with chloroform and B 90 1, 970 4.133 5-3 4;" 2.817 2.1127 C 90 2,017, 4' 137 i 530 a mm mm allowed to stand for about 16 hours. The solu 90 1'96" 1 4.160 543 I 4.397 3, tion was filtered and the filtrate extracted with E 90 1.943 1 7 1 5511 I 4.130 W) 70 a dilute solution of ammonium hydroxide.

-- Thereupon the filtrate was placed on a steam It is obvious from the above data that an ali bath and the chloroform evaporated. Approxiphatic ketone-aromatic amine condensation mately 70% of the original sticky resinous prodproducts age resistant properties are appreciably uct was recovered as a soft brown resinous maintensified by substituting a portion of said con- 75 terial.

aeeaeee The above described brown resinous material was mechanically mixed with the p-amino biphenyl-acetone condensation product, described by J. R.'Ingram, U. S. Patent 2,062,885, in varinew antioxidant composition containing the above described aliphatic ketone-aromatic amine condensation product and the'above described solvent treated phenol-bis N,N'-(benzothiazyl ous proportions and the mixtures incorporated thio methyl) urea reaction product readily dis- In the usual manner in a hevea rubber stock persed in the unvulcanized stock. 1 suitable for the carcass of an automobile tire, .These novel resinous compositions which apcomprising preciably improve the antioxidant and flex-re- Stocks F G H I K Parts Parts Parts Parts Parts 01! bu y by bv weight weight weight weight weiaht Smoked sheets rubber 100. 100. 100.! 100. I. 100. Zinc oxide 30. 30. 30. 30.' 30. Goal tor 011.... 3. 3. 3. 3. 3. Sulfur 2.5 2.5 2.5 2.5 2.5 Stearic acid 1. s 1.5 1. s 1. 5 1.5 Diphenyl guanidine phthalat 0. 4 0. 4 0. 4 0.4 0. 4 Benzothiazyl thio benzoate. D. 3 0.3 0. 3 0. 3 0.3 Amino bipheuyl-acetone condensation roduct 1.0 0.75 0.5 P enol-bis N,N'-(2-benzothiazyl thio v methyl) urea soft brown resinous reaction product of Example 4 .V 0. 0. 5 l. 0

The respective stocks so compounded were 25 sistant properties of aliphatic ketone-aromatic then vulcanized by heating in a press for various periods of time at 126 C. Test strips were cut from the vulcanized stock and artificially aged for 9 hours in an air bomb at 1 2l C. under 80 pounds per square inch pressure. Test data of 0 ergism. As exemplary of this particular emthe respective stocks are set forth below:

amine condensation products-may be further reacted and the resultant products when employed in conjunction with an aliphatic ketone-aromatic amine condensation product still exhibit synbodiment, the following is illustrative.

Table III Ulti- Modulus (lbsJin. at Elongations oi Ulti- Mins. mam mate Sm $353 3 Tensile, P

300% 500% lbs/in 1 percent Unaged, 285..-.. Unagccl, 1,158... 3,952 710 45 Aged, 2l2 Aged, 912 1.635 615 45 Unagcd, 350 7 45 Aged, 342 5'37 45 Unagcd, 385. H5 45 Aged, (31 572 45 Unaged, 362 100 45 d 287 45 Una zed, 308 713 '45 Aged, 188, 540 Una ed, 397 662 60 Aged, 253. .172 60 Unused, 413 662 60 Aged, 32S 582 60 Unaged. 435 658 60 Aged, 383. I 578 so Unaged. 413. 668 60 Aged, l88 300 60 Unaged, 415. 660 60 Aged. I60 Ase 1X0 315 U nngcd, 407 Un'igcd, 1,477. 3, 682 658 JO Aged, 227. Aged, 1,008 1.230 542 90 Unaged, 3S5. Unaged, 1,472 3, 585 650 90 Aged, 307. Aged, 1,163 l, 530 555 E 0 Unused, 41 Unmzed, 1,530 3.858 658 JO Aged, Aged, 1,383 1,815 572 90' 'Unagcd, 365. Unagcd, 1,257 3,317 652 90 Aged, 21 Aged 215 303 90 Unaged, 425 i. Unagcd, 1,562 3.957 662 90 Aged, Aired 463 425 Observing the tensile strengths and moduli of stocks G and H as compared to stock F-in the above table, it is obvious that mixtures of an aromatic amine-aliphatic ketone condensation product and the product of the reaction of a hydroxy aromatic hydrocarbon with an N42- thiazyl thio methyl) urea are markedly superior in age resistance properties to an equal weight of an aromatic amine-aliphatic ketone condensation product (stock F). It should also be observed that stock I containing one part by weight of the phenol-N-(2-thiazyl thio methyl) urea reaction product and no amine-ketone condensation product possesses poorer aging properties than the control stock (stock K). This 37 parts by weight of the sticky brown resinous product of Example 1 was placed in a suitable reaction vessel containing 41 parts by weight (substantially 0.5 mol) of a 37% solution of formaldehyde and 1 part by weight of hexamethylene tetramine. The reaction flask was placed on a steam bath and heated for 24 hours with agitation. Upon cooling, 47.6 parts by weight of a hard brittle resin was obtained.

The above described brittle resinous material was mechanically mixed respectively with the p-amino b'iphenyl-acetone acetone condensation product, described by J. R. Ingram, U. SLPatent 7 2,062,885, and with the diphenylamine-acetone condensation product, described by W. P. ter Horst, U. S. Patent 1,807,355, and the mixtures incorporated in the usual manner in a hevea rubber stock suitable for the tread portion of an automobile tire comprising.

The components of the new antioxidant composition may be employed in ratios and amounts other than those described above in the specific examples. Particularly good results are 'obtained when substantially equal amounts of aliphatic ketone-aromatic condensation product L M N o r R B Paris by Paris by Paris by Paris by Paris by Paris by Parts by weight weight weight weight weight weight weight Smoked sheetsrubben. 100. 100. 100. 100. 100. 100. 100. Carbon black 50. 50. 50. 50. 50. 50. 50. Zinc oxide 5. s. 5. a. 5. 5. 5. Pine tan-.- 2. 2. 2. 2. 2. 2. 2. Sulfur a. a. 3. a. s. s. a. Stearic acid. '3. 3. 3. 3. 3. 3. 3. Mercaptobenzothiazole. 0.76 0. 75 0.75 0.75 0.75 0.75 0.75 p-Amino biphenylacetone reaction to u 0.5 1.0 0.5 D phenylamine-acetone reaction prod- 0.5 1.0 0.5 -The brittle resinous materialoiExample5- 0.5 0.5

, The respective stocks so compounded were and hydroxy aromatic hydrocarbon-N-(Z-thiazyl then vulcanized by heating in a press for 60 thio methyl) urea reaction product are employed. minutes at 135 C. Test strips were cut from By the term rubber as employed in the the vulcanized stocks and artificially aged for 9 specification and appended claims, unless otherhours in an air bomb at 121 C. Test data of wise modified, is intended to be used in its the respective stocks are set forth below: generic sense to include rubber substitutes, nat- Table IV ural rubber, synthetic rubber, and the like. whether or not admixed with fillers, pigments, Mod 1 1 accelerators, etc. Min 31; um. figj By the term treating" as employed in the ap- 8 wk can; Etmgatmns Teinsile ftj pended claims is intended to be used in its generic t 6 fi i fi 5&5; 35 sense to embrace the incorporation of the anti- 3009 500.7 Perm aging oxidant into a rubber or rubber-like substance 0 0 by milling or mastication, its addition to rubber 60 1,607 3,667 4,560 600 693 latices, an? tamghequivzglent grocedufe 5110!; as 0 1.488 31 4,550 620 1.810 app ying i o e sur ace 0 a vu canize or 28 21"3 2196 2 223 i123 40 unvulcanized rubber in the form of a powder or :3 tea i223 pasteoo 1:648 31620 41790 020 21034 While certain specific embodiments of this invention have been disclosed herein, it is to be From the above data it is readily concluded understood that the invention is not limited for that an aliphatic vketone-aromatic amine conmany modifications including substitution of madensation product's antioxidant properties are terials having equivalent chemical properties and pp i y Increased y i y blendmg With varying the proportion of materials used such as modlfied hydroxy aromatlc vd the amount and type of vulcanization accelerator thiazyl thio methyl) urea reaction product. may be done without departing from the spirit Hydroxy aromatic hydrocarbons, other than 5o Scope of the invention the above described, which when reacted with What is claimed an N'm-timazy} thlo methyl) urea W Produce 1. The method of preserving a rubber which readily dispersible compositions which improve com prises treating a rubber with both an antithe antioxidant properties of aliphatic ketoneoxidant which is the condensation roduct of aromatic amine condensation products are catean H h k to d p chol .the naphthols p-tertiary butyl phenol a p a an an P i w1th a synergist for the antioxidant which 15 thymol, carvacrol, the cresols, the xylenols, th d d t b th guaiacol, pyrogallol and the like. 8 con en.sa.lon pm uc of a mem er of 8 Among the N (2' thiaZy1 thio methyl) ureas group consisting of alpha-naphthol, beta-naphthol, and an hydroxy substituted benzene conother than bis N,N -(2-benzothiazyl thio methyl) no t ammg at least one but not more than three urea which are satisfactory are N-(2-th1azol1nyl h drox mu and t 1 t th h thio methyl) urea and thiourea, N-(4,5-dimethyl, y f g p5 eas ree Ydmgep atoms linked to nuclear carbon atoms, the radi- 2-thiazyl thio methyl) urea and thiourea, N-(4- cals linked to the remaining carbon atoms of the ethyl, 2-th1azyl th1o methyl) urea and thiourea, nucleus bein S 1 t d f m and the reaction products of mercapto arylene f h d g 1 e 1.01m e conflstmg thiazoles with methylol carbamides and methylol g y m s cmtammg 3 thiocarbamides as described and disclosed by f a igg and methoxy radlcalsi R.L. Sibley, U. s. Patent 2,145,808. a pmm 8 general frmu1a The components of the new antioxidant com- X position, namely the ketone-amine condensation product and the hydroxy aromatic hydrocarbon- T S NH g NH CH S T N-(Z-thiazyl thio methyl) urea reaction product, where T is an arylene thiazyl radical and X is ;may be added separately but are preferably inan element of group VI of the periodic table .timately mixed by fusi n or mech l l e having an atomic weight less than 33, the ratio before they are incorporated in the rubber. 76 of antioxidant to synergist being within the range of one to three parts antioxidant to one part synergist by weight. 4

2. The method of preserving a rubber which comprises treating a rubber with both an antioxidant which is the condensation product of an aliphatic ketone and an aromatic amine and with a synergist for the antioxidant which is the condensation product of a benzene hydrocarbon containing not more than ten carbon atoms having at least three unsubstituted nuclear positions and containin at least one but not more than three of the nuclear hydrogen atoms sub- 'stituted by hydroxy groups and a compound of the general formula where T is an arylene thiazyl radical and X is an element of group VI of the periodic table having an atomic weight less than 33, the ratio of antioxidant to synergist being within the range of one to three parts antioxidant to one part synergist by weight.

3. The method of preserving a rubber which comprises treating a rubber with both an antioxidant which is the condensation product of an aliphatic ketone and an aromatic amine and with a synergist for the antioxidant which is the condensation product of a monohydric phenol containing not more than ten carbon atoms in which the hydroxyl group is linked to a hydrocarbon group consisting in a benzene ring containing at least three unsubstituted positions and a his N,N'-(2-arylenethiazylthiomethyl) urea, the ratio of antioxidant to synergist being within the range of one to three parts antioxidant to one part synergist by weight.

- 4. The method of preserving a rubber which comprises treating a rubber with a composition comprising a rubber antioxidant which is the condensation product of an aliphatic ketone with an aromatic amine and a synergist for the antioxidant which is the reaction product of resorcinol with his N,N'-(2-benzothiazyl thio methyl) urea the ratio of antioxidant to synergist being within the range of one to three parts antioxidant to one part synergist by weight.

'5. The method of preserving a rubber which comprises treating a rubber with a composition comprising a rubber antioxidant which is the condensation product of an aliphatic ketone with an aromatic amine and a synergist for the antioxidant which is the reaction product of hydroquinone with his N,N-(2-benzothiazyl thio methyl) urea the ratio of antioxidant to synergist being within the range. of one to three parts antioxidant to one part synergist by weight.

6. The method of preserving a rubber which comprises treating a rubber with a composition comprising a rubber antioxidant which is the condensation product of an aliphatic ketone with an aromatic amine and a synergist for the antioxidant which is the reaction product of phenol with his N,N'-(2-benzothiazyl thio methyl) urea the ratio of antioxidant to synergist being within the range of one to three parts antioxidant to one part synergist by weight.

'7. The method of preserving a rubber which comprises treating a rubber with a composition comprising a rubber antioxidant which is the condensation product of acetone with p-amino biph'enyl and a synergist for the antioxidant which is the reaction product of his N,N'-(2-benzothiazyl thio methyl) urea with resorcinol the ratio of antioxidant to synergist being within the range of one to three parts antioxidant to one part synergist by weight.

8. They method of preserving a rubber which comprises treating a rubber with a composition comprising a rubber antioxidant which is the condensation product of acetone with p-amino biphenyl and a synergist for the antioxidant which is the reaction product of his N,N'-(2- benzothiazyl thio methyl) urea with hydroquinone the ratio of antioxidant to synergist being within the range of one to three parts antioxidant to one part synergist by weight.

9; The method of preserving a rubber which comprises treating a rubber with a composition comprising a rubber antioxidant which is the condensation product of acetone with p-amino biphenyl and a synergist for the antioxidant which is the reaction product of his N,N'-(2- benzothiazyl thio methyl) urea with phenol the ratio of antioxidant to synergist being within the range of one to three parts antioxidant to one part synergist by weight.

10. The vulcanized rubber product obtained by treating a rubber with both an antioxidant which is the condensation product of an aliphatic ketone and an aromatic amine and with a synergist for the antioxidant which is the condensation product of a member of the group consisting of alpha-naphthol, beta-naphthol, and an hydroxy substituted benzene containing at least one but not more than three hydroxy groups and at least three hydrogen atoms linked to nuclear carbon atoms, the radicals linked to the remaining carbon atoms of the nucleus being selected from the group consisting of hydrogen, alkyl radicals containing not more than four carbon atoms and methoxy radicals, and a compound of the general formula where T is an arylene thiazyl radical and X is an element of group VI of the periodic table having an atomic weight less than 33, the ratio of antioxidant to synergist being within the range of one to three parts antioxidant to one part synergist by weight.

11. The vulcanized rubber product obtained by treating a rubber with both an antioxidant which is the condensation product of an aliphatic ketone and an aromatic amine and with a synergist for the antioxidant which is the condensation product of a benzene hydrocarbon containing not more than ten carbon atoms having at least three unsubstituted nuclear positions and containing at least one but not more than three of the nuclear hydrogen atoms substituted by hydroxy groups and a compound of the general formula where T is an arylene thiazyl radical and X is an element of group VI of the periodic table having an atomic weight less than 33, the ratio of antioxidant to synergist being within the range of one to three parts antioxidant to one part synergist by weight.

12. The vulcanized rubber product obtained by treating a rubber with both an antioxidant which is the condensation product of an aliphatic ketone and an aromatic amine and with a synergist for the antioxidant which is the condensation product of a monohydric phenol containing not more than ten carbon atoms in which the hydroxyl group is linked to a hydrocarbon group 11 consisting in a benzene ring containing at least three unsubstituted positions and a his N;N'-(2- arylenethiazylthiomethyl) urea, the ratio of antioxidant to synergist being within the range of one to'three parts antioxidant to one part synergist by weight.

13. The vulcanized rubber product obtained by treating a rubber with a composition comprising a rubber antioxidant which is the condensation product of an aliphatic ketone with an aromatic amine and a synergist for the antioxidant which is the reaction product of resorcinol with bis N,N'-(2-benzothiazyl thio methyl) urea the ratio of antioxidant to synergist being within the range of one to three parts antioxidant to one part synergist by weight.

14. The vulcanized rubber product obtained by treating a rubber with a composition comprising a rubber antioxidant which is the condensation product of an aliphatic ketone with an aromatic amine and a synergist for the antioxidant which is the reaction product of hydroquinone with his N,N'-(2-benzothiazyl thio methyl) urea the ratio of antioxidant to synergist being within the range of one to three parts antioxidant to one part synergist by weight.

15. The vulcanized rubber product obtained by treating a rubber with a composition comprising a rubber antioxidant which is the condensation product of an aliphatic ketone with an aromatic amine and a synergist for the antioxidant which is the reaction product of phenol with his N,N'- (2-benzothiazyl thio methyl) urea the ratio of antioxidant to synergist being within the range 17. The vulcanized rubber product obtained by V treating a rubber with a composition comprising of one to three parts antioxidant to one part synergist by weight.

16. The vulcanized rubber product obtained by treating a rubber with a composition comprising a rubber antioxidant which is the condensation a rubber antioxidant which is the condensation product of acetone with p-amino biphenyl and a synergist for the antioxidant which is the reaction product of his N,N'-(2-benzothiazyl thio methyl) urea with hydroquinone the ratio of antioxidant to synergist being within the range of one to three parts antioxidant to one part synergist by weight.

18. The vulcanized rubber product obtained by treating a rubber with a composition comprising a rubber antioxidant which is the condensation product of acetone with p-amino biphenyl and a synergist for the antioxidant which is the reaction product of his N,N-(2-benzothiazyl thio methyl) urea with phenol the ratio of antioxidant to synergist being within the range of one to three parts antioxidant to one part synergist by weight. I

A MARION W. HARMAN.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,782,842 Cronshaw et a1 Nov. 25, 1930 1,805,194 Strickhouser May 12, 1931 2,062,885 Ingram Dec. 1, 1936 2,145,808 Sibley Jan. 31, 1939 

1. THE METHOD OF PRESERVING A RUBBER WHICH COMPRISES TREATING A RUBBER WITH BOTH AN ANTIOXIDANT WHICH IS THE CONDENSATION PRODUCT OF AN ALIPHATIC KETONE AND AN AROMATIC AMINE AND WITH A SYNERGIST FOR THE ANTIOXIDANT WHICH IS THE CONDENSATION PRODUCT OF A MEMBER OF THE GROUP CONSISTING OF ALPHA-NAPHTHOL, BETA-NAPHTHOL, AND AN HYDROXY SUBSTITUTED BENZENE CONTAINING AT LEAST ONE BUT NOT MORE THAN THREE HYDROXY GROUPS AND AT LEAST THREE HYDROGEN ATOMS LINKED TO NUCLEAR CARBON ATOMS, THE RADICALS LINKED TO THE REMAINING CARBON ATOMS OF THE NUCLEUS BEING SELECTED FROM THE GROUP CONSISTING OF HDROGEN, ALKYL RADICALS CONTAINING NOT MORE THAN FOUR CARBON ATOMS AND METHOXY RADICALS, AND A COMPUND OF THE GENERAL FORMULA 